Circuit breaker with ambient temperature compensation



F. B. DESIO 3, 3

CIRCUIT BREAKER WITH AMBIENT TEMPERATURE COMPENSATION Feb. 8, 1966 FiledNov. 28, 1960 N V EN TOR.

Frail/ Bfiedzio um l i -/I/ I I .-Z/ ,M mg;

United States Patent 3,234,348 CIRCUIT BREAKER WITH; AMBIENT TEMPERATURECOMPENSATION Frank B. Desio, Melrose Park, Ill., assignor. toLittelfuse, Inc, DesPlaines, Ill, a corporation of Illinois NOY- 2' 60;g i- N9. 8 Cla ms (01,-. ZQQ l -Q) This.v invention relates to circuitbreakers of the resettable ype w c p d ta ome Pr dstflmimd increase inrated current to open the circuit automatically and which, in addition,include provision for compensation in, accordance with the ambienttemperaure. 'ljhus, the value of or range of overload current for whichthe device is designed will remain substantially unafiected due tovariation. in ambient temperature.

The invention device is capable of being initially calibrated to, openthe circuit at some predetermined'value of overload current or may belater adjusted, within limits, to. operate at some other. value of overload current.

Among the objects of the invention are the. provision of a Circuit b ethe e e al. c ass. a a ss l fuh qh.

is Simple in o s s an reliable in q e a a Pro id s good wiping action ofthe contacts when released and when reset, and may be easily adjusted toobtain circuit opening action within the range of values of overloadcurrent which the device is intended to accommodate. Generally arded thnvent de in n aspa comprises n in a p as whia u p rts a p of m na wh r yha' v s ay e assed in e s in the cui a d u er nd 9W? b m al switchmembers bearing mutually latching contacts. These latter are providedwith faces adapted to abut to complete the circuit for normal currentflow and to release when overload current is applied. lfor low, currentapplications, at least one of the switch members is not adapted to carrythe current through the switch whereas the other switch member may carrycurrent. The configuration of the switch members, their lamina,- tionsand relative position are so selected that, when influenced by changesin ambient temperature they move in unison to preserve their latchedcondition but will operate to unlatch in response to the overloadcurrent. By providing an electric heater in heat-transferring relationwith the switch member not carrying current and passing the currentthrough the heater, the switch may be rendered more sensitive to lowoverload current without afiecting that function of the switch membersproviding accommodation to change in the ambient temperature.

In another aspect the invention comprises simple, inexpensive means forrapid initial calibration of the device or for subsequent recalibrationthereof.

A reset button is provided for relatching the contacts followingabatement of the overload condition, this button desirably being carriedin a cover secured to the insulating base and having associatedtherewith bias means for maintaining the button in a normal position.

Other objects and advantages of the invention will become apparent fromthe ensuing description which, taken with the accompanying drawing,discloses a preferred form in which the invention may be embodied inpractice.

In this drawing:

FIG. 1 is a perspective view of the device its errc i pec FIG. 2 is alongitudinal medial cross section through the device showing the switchopen;

FIG. 3 is a cross section, on somewhat reduced scale, taken on the line3-3 ofFIG. 2; and

FIG. 4 is a view similar to that of FIG. 2 showing the switch closed andthe resetbutton partially operated, as in the resetting operation. '7

Turning to the drawing, I have shown a circuit breaker in accordancewith the principles of the invention comprising a base 10 of suitableelectrically-insulating material having an elongated recess Q and athrough aperture 11 adjacent one end "for passage of a rivet 12 orequivalent fastening means. The terminals 15' and 16 each pass throughrespective apertures 17 and18, in they base 10 and are desirably bentover at their inner ends to provide portions for a purpose to appear.Otherwise the terminals rnay take any of available conventional formsand arrangement. i i

A lower switch member 25 comprises a bimetallic strip as customarilyemployed for the basic function of the member, namely transversemechanical fiexure in response to change in temperature and, since suchconstruction is common per se, the laminations are not illustrated indetail. However, at this juncture, it is pointed out that the member isso constructedand positioned that increase in temperature will causeflexure of the principal or horizontal portion 25a thereof, downwardly'as indicated by the arrow 1 and, upon decrease in temperature, inthe direction D. At the same time, the vertical portion 25b moves ordeflects in the respective directions I and as shown. Portion 21 ofterminal 15 is current carrying relation with member 25. The member- 25is of relatively large cross sectional dimensions so that the passage ofcurrent therethrough will have substantially no effect upon thetemperature thereof.

An insulating spacer or block 31 is received in and held againstrotation by the recess 9 in the base 10. A projection 32 on the base 10and a corresponding recess in the block 31 prevents longitudinalmovement of the block 21 with respect to the base 10. Assuming that thestack assembly is complete and under the tension of the rivet 12 theblock 31 maintains the member 25 in operative position and abuttingportion 21 of the terminal 15.

Means are provided for shifting the member 25 longitudinally to alterthe degree of latching engagement of the contacts to be subsequentlydetailed and hence, the response of the switch. For example, theanchored end of the member is illustrated as provided with a lengthwiseslot 36 slidable on the sides of the projection 32, and a more or lesscentrally positioned aperture 37 confronting an access opening 38 in thebase 16 for engagement by a tool passed through the aperture is providedtov shift the member 25 lengthwise for calibration purposes. Thepressure applied to the secured end of the member 25 is, as will appear,of a character permitting such adjustment and its reliable retentionnotwithstanding repeated operation of the device.

The other switch member 41, cooperative with the member 25, is alsobimetallic and of the same general character as the member 25 exceptthat it is arranged to flex in such manner that the generally horizontalportion 41;: thereof moves upwardly upon increase in tempertaure, asindicated by the arrow 1, and in the direction of the arrow D upondecrease in temperature; while the substantially vertical portion 41b ofthe member 41 deflects in the respective directions I and D Each of themembers 25 and 41 is provided at its free or distal end with respectivecontacts 43 and 44 having mutually camming faces 43a and 44m andlatching faces 43b and 44b. FIG. 2 shows the members unlatehed, i.e.,the circuit is broken and FIG. 4 shows the same latched, i.e., thecircuit is closed.

It will be noted that member 41 is provided with an anchoring end 51apertured to pass the rivet 12 and bent Patented Feb, 8, 1966 separatedtherefrom by an insulator 67, is the bent portion 22 of the terminal 16which extends to a position whereat connection thereto of a heaterwinding 53 may be made, as by welding or soldering at 54. Terminal 16 issuitably located on the block 31 by a projection 55 thereof receiving amating opening 56 in the portion 2 2.

Lateral positioning of the switch member 41 and the reset mutton spring61 (to be alluded to later) is achieved by flanking, upstanding posts 57(FIG. 3) preferably formed integrally with the block 31. Theleaf spring61 is desirably dished in the region 63 overlapped by the head of therivet 12 in order that, when the latter is suitably upset the region 63serves as a compression spring maintaining, in a simple, inexpensivemanner, the parts 15, 16, 25, 31, 41, 61 and 67 in proper operatingrelationship.

Heating element 53 is preferably in the form of ahelical windingpositioned over the member 41 over the greater part of its length andembracing the portions 41a and 41b thereof. To obtain optimum heattransfer the several coils are flattened into intimate contact with theswitch members, or the element may be initially wound in coils of flatoval configuration. 7 Such element is of any well-known type, e.g.,Nichrome suitably insulated to avoid short-circuiting or miniaturizedversion of the wellknown Calrod elements available from General ElectricCo., and has its ends bared and connected respectively to the portion41b at 65 and the bent-over leg 22 of the terminal 16 at 54. endconnection may be availed of so long as the current through the switchmember 25 and contacts 43 and 4.4 also traverses the heater winding. Itwill also be clear that the heating element must be sufficientlyflexible over its length as not to inhibit flexure of the member 41 inresponse to variation in temperature. The insulator 67 interposedbetween the member 41 and leg 22 insures that line current does not passthrough the member 41.

A cover 71 is secured to the base 10, as by cars 72 extending throughnotches in the base and bent under the base, to enclose the parts of theassembly, other than the terminals 15 and 16 and the reset button 75.This latter is of insulating material and is guided in a sleeve 76formed in the top of the cover 71 for free sliding movement. A head 79limits outward displacement, and retention of the button in its normal,i.e., upper, position is the result of upward bias applied by the leafspring 61. The button is so positioned that, when actuated it will abutthe switch member 41 at approximately the highest point thereof, namelythe junction of the portions 41a and 41b thereof, although other formsof reset means may be availedof.

Assuming that the device is connected in circuit and has been operatedto closed condition (FIG. 4) by thrusting the reset button 75 inwardlyagainst the bias of the restoring spring 61 and that of the members 41,the contacts 43 and 44 will be interengaged. Such action occurs as aresult of the camming surfaces 43a and 44a sliding one on the other anddeforming the respective members 25 and 41 momentarily until latchingoccurs, whereafter the contact surfaces 43b and 44b remain latched,during normal or rated current flow, to complete the circuit. Followingclosure of the contacts the button 75 is released and is restoredoutwardly by the spring 61.

In the absence of overload current any change in ambient temperature isineffective to unlatch the contacts. As stated hereinbefore thebimetallic character oft-he members 25 and 41 is such that increase inambient temperature will flex member portion 25a downwardly (I) andportion 25b'outwardly (I) while member portion 41a will flex upwardly (Iand portion 41b also outwardly (I Accordingly, the compensating functionjust described maintains the contacts 43 and 44. latched It will beapparent that other forms of V the circuit (FIG. 3).

in a substantially constant degree of overlap. Upon decrease in ambienttemperature the situation is reversed (arrows D and D and compensationprevails.

However, upon flow of overload current the heater Winding 53 isinstrumental in causing a rapid rise in temperature of the switch member41. Heating of the portion 41a operates to increase the contact pressurebetween the contact latch surfaces 43b, 44b, and when the portion,

41b is heated sufficiently to disengage the contact latch surfaces 43b,44b, the contacts 43 and 44 are released with a snap action for rapidand non-arcing interruption of Reset, following relief of overload, isbelieved to be obvious from the preceding description in reference toFIG. 4. If the reset button 75 is pushed in all the way, the contacts 43and 44 will be separated and the circuit opened. Thus, it is impossibleto hold the circuit closed by pressing on the reset button, andtrip-free resetting is thereby provided. The contacts 43 and 44 cannotbe relatched until the bimetallic member 41 is cooled sufliciently toallow relatching thereof. It the overload condition still persists uponresetting, the contacts 43 and 44 will immediately release to again openthe circuit.

From the foregoing it will have become apparent that the inventiondevice is characterized by reliable compensation in accordance withvariation in ambient temperature and rapid, non-arcing opening of thecircuit. Moreover it will be seen that as long as overload subsists thedevice may not be latched in closed position or held in closed positionby improper, sustained application of pressure on the reset button for,in such case, the contacts 43 and 44 continue to remain separated andcannot be re-latched until the overload current is reduced to normal.Thereupon, cooling of the switch member 41' and the heater winding 53will allow the contacts to resume a relative position permittingrelatching.

For higher current applications, the heater 53 may be eliminated, andthe load current passed directly through the bimetallic member 41 fordirectly heating the same. In this connection the insulator 67 isomitted so that electrical contact is made between the member 41 and theportion 22 of the contact 16. The cross sectional dimensions of themember 41 are relatively small, so that the resistance to current flowtherethrough directly heats the member 41 to separate the contacts 43and 44 upon the occurrence of an oveload condition. Outside of directlyheating the member 41, the operation of this arrangement is the same asdescibed above and accordingly a further description of the operation isnot considered necessary.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

I claim:

1. An ambient temperature compensated circuit breaker comprising: abase, first and second resilient switch members cantilever-mounted at acommon end to said base and electrically insulated thereat, both memberscomprising laminated material differentially expansible to flex themember transversely when subjected to change in temperature, each memberhaving its free end bent substantially perpendicularly to the remainderthereof, said bent portions being substantially confronting and eachbeing provided with a contact at the free end thereof, said contactseach having a face adapted for mutual overlapping latching engagementwhen the circuit is closed and a camming face adapted for mutual slidingabutment to dis the laminated material comprising each member being suchthat,-up on variation in ambient temperature, the

bers cantilever mounted at a common end to said base and electricallyinsulated thereat, both members comprising laminated materialdifferentially expansible to flex the member transversely when subjectedto change in temperature, each member having its free end bentsubstantially perpendicularly to the remainder thereof, said bentportions being substantially confronting and each being provided with acontact at the free end together adapted to engage overlappinglylatchingly to maintain closed condition of the breaker when the freeends of the members are brought together, the respective arrangement ofthe laminated material comprising each member being such that, uponvariation in ambient temperature, the members flex in respectiveopposite directions and the bent end portions of the members flex inrespective same directions and degrees to preserve a substantiallyconstant degree of overlapping latching engagement of the contacts and,upon passage of overload current through the members, the members andtheir bent end portions will flex in a direction to release theoverlapping latched condition of said contacts, and means for connectingsaid members in the circuit.

3. A circuit breaker in accordance with claim 1 wherein means areprovided for longitudinally adjusting said resilient switch members withrespect to each other to adjust the degree of overlapping latchingengagement of the contacts for calibration purposes.

4. A circuit breaker in accordance with claim 2 wherein means areprovided for longitudinally adjusting said resilient switch members withrespect to each other to adjust the degree of overlapping latchingengagement of the contacts for calibration purposes.

5. An ambient temperature compensated circuit breaker for a circuit tobe protected comprising: a base, a first resilient bimetallic membercantilever mounted at one end on said base and having its free end bentsubstantially perpendicularly to the remainder thereof to form asubstantially perpendicular leg at its free end, a contact having alatch surface carried by the outside of said leg, 21 second resilientbimetallic member cantilever mounted at one end on said base adjacentthe mounting of the first bimetallic member and having its free end bentsubstantially perpendicularly to the remainder thereof to form asubstantially perpendicular leg at its free end, a contact having alatch surface carried by the inside of the leg of said second bimetallicmember, the latching surfaces of said contacts normally overlapping andengaging each other against the resiliency of the bimetallic members forcompleting the circuit being protected, said second bimetallic memberoperating upon an increase in temperature to tend to move away from thefirst bimetallic member and to move the inside contact thereof outwardlywith respect to the outside contact of the first bimetallic member, saidfirst bimetallic member operating upon an increase in temperature totend to move away from the second bimetallic member and to move theoutside contact thereof outwardly with respect to the inside contact ofthe second bimetallic member to maintain the overlap of said contactssubstantially constant regardless of ambient temperature conditionsatfecting said first and second bimetallic members, said secondbimetallic member being heated by the current flow in the circuit to beprotected and being operative upon an excessive current flow to move thelatching surface of its contact out of engage- 6, ment with the latchingsurface of the contact of the first bimetallic member to allow thebimetallic elements to spread apart and break the circuit.

6, A circuit breaker in accordance with claim 5 including means forlongitudinally adjusting said bimetallic members with respect to eachother to adjust the amount of overlap of the latch surfaces of thecontacts for calibration purposes.

7. An ambient temperature compensated circuit breaker for a circuit tobe protected comprising, a base having a plurality of openings therein,a first terminal extending through one of the base openings and engagingthe interior of the base, a first resilient bimetallic member overlyingat one end the first terminal and having its free end bent substantiallyperpendicularly to the remainder thereof to form a substantiallyperpendicular leg at its free end, an insulating block overlying saidone end of said first resilient bimetallic member, a second terminalextending through another of the base openings and overlying the block,a second resilient bimetallic member overlying at one end the secondterminal and having its free end bent substantially perpendicularly tothe remainder thereof to form a substantially perpendicular leg at itsfree end, a dished resilient member overlying said one end of saidsecond resilient bimetallic member, a rivet extending through another ofthe base openings, said first terminal, said first end of said firstresilient bimetallic member, said insulating block, said secondterminal, said first end of said second resilient bimetallic member, andsaid dished resilient member for resiliently clamping the same together,a contact having a latch surface carried by the outside of theperpendicular leg on said free end of said first resilient bimetallicmember, a contact having a latch surface carried by the inside of theperpendicular leg on said free end of said second resilient bimetallicmember, said latch surfaces of said contacts normally overlapping andengaging each other against the resiliency of the bimetallic members forcompleting the circuit being protected, said second bimetallic memberoperating upon an increase in temperature to tend to move away from thefirst bimetallic member and to move the inside contact thereof outwardlywith respect to the outside contact of the first bimetallic member, saidfirst bimetallic member operating upon an increase in temperature totend to move away from the second bimetallic member and to move theoutside contact thereof outwardly with respect to the inside contact ofthe second bimetallic member to maintain the overlap of said contactssubstantially constant regardless of ambient temperature conditionsaffecting said first and second bimetallic members, said secondbimetallic member being heated by the current flow in the circuit to beprotected and being operative upon an excessive current flow to move thelatching surface of its contact out of engagement with the latchingsurface of the contact of the first bimetallic member to allow thebimetallic elements to spread apart and break the circuit.

8. A circuit breaker in accordance with claim 7 wherein said firstresilient bimetallic member has a hole overlying another opening in thebase for receiving a tool projected through said base opening forlongitudinally shifting said first resilient bimetallic member withrespect to said second resilient bimetallic member for calibrationpurposes.

References Cited by the Examiner UNITED STATES PATENTS 1,431,220 10/1922 Donle 200--116 1,948,938 2/1934 Lawton 200-116 2,023,517 12/1935Creager 200166 2,148,600 2/1939 Beckler 200-116 2,261,366 11/1941 Grout200138 2,277,443 3/ 1942 Livingston 200--166 2,293,671 8/1942 Alexander2001l6 (Other references on following page) 7 UNITED STATES PATENTSDafiorn 200--138 Howard 200138 Baker 200166 Tucker 2001 16 Marcoz200-116 Elliott 200-116 Chase et a1 200166 8 2,831,090 4/1958 Kueser200138 3,038,047 6/1962 Marquis 200116 FOREIGN PATENTS 597,603 9/1925France. 7 513,143 10/1939 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

RICHARD M. WOOD, Examiner.

1. AN AMBIENT TEMPERATURE COMPENSATED CIRCUIT BREAKER COMPRISING: A BASE, FIRST AND SECOND RESILIENT SWITCH MEMBERS CANTILEVER-MOUNTED AT A COMMON END TO SAID BASE AND ELECTRICALLY INSULATED THEREAT, BOTH MEMBERS COMPRISING LAMINATED MATERIAL DIFFERENTIALLY EXPANSIBLE TO FLEX THE MEMBER TRANSVERSELY WHEN SUBJECTED TO CHANGE IN TEMPERATURE, EACH MEMBER HAVING ITS FREE END BENT SUBSTANTIALLY PERPENDICULARLY TO THE REMAINDER THEREOF, SAID BENT PORTIONS BEING SUBSTANTIALLY CONFRONTING AND EACH BEING PROVIDED WITH A CONTACT AT THE FREE END THEREOF, SAID CONTACTS EACH HAVING A FACE ADAPTED FOR MUTUAL OVERLAPPING LATCHING ENGAGEMENT WHEN THE CIRCUIT IS CLOSED AND A CAMMING FACE ADAPTED FOR MUTUAL SLIDING ABUTMENT TO DISPLACE EACH OTHER MUTUALLY AS AT LEAST ONE OF THE MEMBERS IS MOVED TO CIRCUIT-CLOSING POSITION, WHEREAFTER SAID LATCHING FACES MUTUALLY OVERLAPPINGLY ENGAGE BY VIRTUE OF THE RESILIENCY OF SAID MEMBERS, THE RESPECTIVE ARRANGEMENT OF THE LAMINATED MATERIAL COMPRISING EACH MEMBER BEING SUCH THAT, UPON VARIATION IN AMBIENT TEMPERATURE, THE MEMBERS FLEX IN RESPECTIVE OPPOSITE DIRECTION AND THE BENT END PORTIONS OF THE MEMBERS FLEX IN RESPECTIVE SAME DIRECTIONS AND DEGREES TO PRESERVE A SUBSTANTIALLY CONSTANT DEGREE OF OVERLAPPING LATCHING ENGAGEMENT OF THE CONTACTS AND, UPON PASSAGE OF OVERLOAD CURRENT THROUGH THE MEMBERS, THE MEMBERS AND THEIR BENT END PORTIONS WILL FLEX IN A DIRECTION TO RELEASE THE OVERLAPPING LATCHED CONDITION OF SAID CONTACTS FOR SEPARATION THEREOF, AND MEANS FOR CONTACTING SAID MEMBERS IN THE CIRCUIT. 